Heave Compensator for Constant Force Application to a Borehole Tool

ABSTRACT

The compensating device has a through passage that goes to the borehole tool. There is a lateral passage to a piston housing. Through the use of a differential piston area on the outer housing, a net uphole force results from backpressure as a result of flow pumped through a section mill that mills in an uphole direction. If the vessel goes down the mill is just pushed away from the tubular being cut. If wave action takes the vessel up fluid is displaced back into the mandrel but the constant force up that is dependent on the existing backpressure in the tubing keeps a steady uphole force on the mill. The tool can be reversed for applications that require a net down force during milling. Rotational locking between the mandrel and the outer housing can be used. Ports are sized to prevent damping responses.

FIELD OF THE INVENTION

The field of the invention is a compensating device that maintains a constant axial force on a borehole tool responsive to internal pressure in the tool created by fluid pumped through the compensating device and bound for the borehole tool.

BACKGROUND OF THE INVENTION

Some borehole procedures such as section milling are sensitive to load variations which could adversely affect the cutting inserts on the mill. Floating vessels are subject to wave action and frequently contain heave compensation devices to even out the up and down motion of the vessel in response to wave action. These systems are not sensitive enough to stop all the force variations at the borehole tool, which can adversely affect the longevity of the tool. Heave compensation systems are large and very complex as illustrated in U.S. Pat. No. 3,905,580; US 2016/0039643; and U.S. Pat. No. 9,267,340. Thrusters are used as compensation device during drilling as illustrated in US 2001/0045300 and U.S. Pat. No. 6,102,138. Still other tool variations for force control during drilling applications are U.S. Pat. No. 7,284,606 and U.S. Pat. No. 6,705,411.

What is provided by the invention is a system that can apply a constant loading force in either a downhole or uphole direction based on internal pressure. The tool has the needed telescoping capability such that between opposed travel limits a predetermined force is applied in tension or compression to the attached borehole tool depending on the orientation of the compensation tool in the tubular string. The fluid pressure that regulates the force applied to the borehole tool is the same fluid pressure that is applied to the borehole tool in the case of a milling tool. The pressure exits nozzles and takes away cuttings. These and other aspects of the present invention will be more readily apparent to those skilled in the art from a review of the description of the preferred embodiment and the associated drawings while recognizing that the full scope of the invention is to be determined from the appended claims.

SUMMARY OF THE INVENTION

The compensating device has a through passage that goes to the borehole tool. There is a lateral passage to a piston housing. Through the use of a differential piston area on the outer housing, a net uphole force results from backpressure as a result of flow pumped through a section mill that mills in an uphole direction. If the vessel moves down the mill is just pushed away from the tubular being cut. If wave action takes the vessel up fluid is displaced back into the mandrel but the constant force up that is dependent on the existing backpressure in the tubing keeps a steady uphole force on the mill. The tool can be reversed for applications that require a net down force during milling. Rotational locking between the mandrel and the outer housing can be used. Ports are sized to prevent damping responses.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a section view of the device in the lowermost position of the vessel;

FIG. 2 is the view of FIG. 1 with the vessel having risen due to wave action;

FIG. 3 is an alternative embodiment to FIG. 1 in the lowermost position of the vessel;

FIG. 4 is the view of FIG. 3 in the uppermost position of the vessel;

FIG. 5 is a section view through line 5-5 of FIG. 4.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1, there is a mandrel 10 having a passage 12 and lateral ports 14. An outer housing 16 surrounds the mandrel 10 and has ports 18 leading to a surrounding annular space 20. A vessel is schematically illustrated as V rides on the water and likely has a heave compensator on board to minimize the movement seen at connection 22 to the mandrel 10. Seals 24 and 26 are different diameters and define a variable volume chamber 28 between the outer housing 16 and the mandrel 10. Pressure applied to passage 12 communicates with chamber 28 to create a net force in the direction of arrow 30 on the outer housing 16. This happens because the piston areas 32 and 48 see passage 12 pressure for a force in the direction of arrow 30 and that force is opposed by pressure in the annulus 20 which is usually far lower acting on surfaces 50 and 52. Ports 18 communicate variable volume chamber 38 with the annular space 20 so that the mandrel 10 does not get liquid locked in housing 16. Seals 26 and 40 seal off chamber 38 from chamber 28 as well as sealing chamber 42 from chamber 38. Chamber 42 has the same pressure as in passage 12 and a series of keyways 44 between which are disposed keys 46 mounted to the mandrel 10. Mandrel 10 is rotationally locked to housing 16 using keyways 44 meshing with a key or keys 46.

Mill M can be of a type that mills under a tensile force. The objective is to maintain a constant tensile force on the mill M during milling. Mill M also uses nozzles to clear milling debris and the pressure drop through those nozzles accounts for the back pressure in passage 12 during milling. With the opposed piston areas 32 on one hand and 34 and 36 on the other hand, the consistent back pressure from flow through passage 12 going to the nozzles of mill M results in a consistent tensile force applied to the mill M during milling. There can be some variation in the annulus 20 pressure but it should not materially affect the net force in the direction of arrow 30 on mill M. In most cases passage 12 pressure acting on area 48 will create a net force in the direction of arrow 30 on housing 16 slightly offset by pressure in annulus 20 acting on area 50.

When the vessel V moves downward due to wave action the vessel's heave compensator can offset some of that motion but there can be a net downward force on the mill in a direction opposite arrow 30. Mandrel 10 has the ability to move down until it shoulders out against shoulder 52. As this happens the pressure in passage 12 continues to provide the net force to the mill M in the direction of arrow 30 so that milling can continue with a uniform uphole force independent of the movement of mandrel 10 until mandrel 10 engages shoulder 52. At that point there is tandem movement of the mandrel 10 and the outer housing 16 which simply results in backing away the mill M from the object or tubular that is being milled.

On the other hand, if the vessel V moves upward raising mandrel 10, there is no effect on the mill M unless shoulder 54 on mandrel 10 engages shoulder 56 on the outer housing 16. The outer housing 16 is designed long enough to prevent these two shoulders from contacting since doing so will increase the stress on the outer housing 16 and the mill M that in the displayed configuration in FIGS. 1 and 2 is already under tension when milling. Movement of mandrel 10 from the FIG. 1 to the FIG. 2 position reduces the volume of chamber 28 and increases the volume of chamber 38. To enable the movement fluid flows into passage 12 through ports 14 and into chamber 38 through ports 18. The volume of chamber 42 increases as it holds at a steady pressure seen in passage 12. The flows reverse when the movement is from the FIG. 2 position back to the FIG. 1 position. As long as the mandrel 10 has room to move between opposed surfaces 52 and 56 the pressure in passage 12 keeps a constant force on the mill M which is determined by the mill nozzle quantity and size and the delivered flow rate to those nozzles that are not shown.

Those skilled in the art will appreciate that the internal configuration of mandrel 10 and outer housing 16 can be changed so that pressure in passage 12 will result in a net downhole force on outer housing 16 if a mill M is used that operates with a compressive load against the piece being milled rather than a tensile force against the piece as shown in FIGS. 1 and 2. The mill M can be operated with rotating drill pipe or equivalent driving system connected to passage 12 on the uphole end and to the nozzles of the mill M on the downhole end.

Those skilled in the art will appreciate that the described device is able to maintain a constant force on a tool in a designated direction whose magnitude depends on the internal pressure pumped to the tool while compensating for vessel movements as the mill operates consistently with a required applied force. As long as the telescoping components have room to move relative, the movement of the vessel will be immaterial to the operation of the mill M. In some applications torque can be transmitted through the tool as its telescoping components can be rotationally locked. The device is simple in construction and needs just three seals for a force to be generated in an uphole direction. To generate a steady force in the downhole direction a single seal is needed. The tool length can be configured to take into account the contemplated movement of the mandrel 10 attached to the vessel V so that the engagement with the travel stops is avoided.

While the layout of FIGS. 1 and 2 result in a tensile force on the mill M, a resulting compressive force can result if the locations of ports 14 and 18 are swapped about the middle seal 26. When that happens the chambers 28 and 38 switch positions although the travel stops 32 and 52 remain in position. Alternatively the mill M can be simply connected at thread 22 and the vessel V connected to the outer housing 16, essentially turning the tool of FIGS. 1 and 2 up side down and the result will still be a tensile force as is now shown.

FIGS. 3-5 show a simplified version of a mandrel 70 surrounded by an outer housing 72. The vessel V is connected at 74 and the mill M is connected at 76. Housing 72 has a passage 78 that continues as passage 80 to the mill M. Pressure in passages 78 and 80 creates pressure in variable volume chamber 82 due to the presence of seal 84. A force in the direction of mill M depicted by arrow 86 is generated for a mill that operates under a compressive force. Housing 72 moves with the vessel V. The FIG. 4 position is reached if the vessel V moves up so that surface 90 hits travel stop 88 on housing 72 although the length of housing 72 can be provided to avoid jarring loads on the mill M. Ideally surfaces 92 and 94 should not contact when the vessel V moves down. As shown in FIG. 5 the mandrel 70 and housing 72 are rotationally locked in this case with matching non-round shapes in the form of hexagons. Other non-round shapes or splined arrangements are also contemplated as alternatives. Variable volume chamber 96 has no seals near its lower end allowing fluid to enter or leave as the volume changes to avoid liquid locking of mandrel 70.

The above description is illustrative of the preferred embodiment and many modifications may be made by those skilled in the art without departing from the invention whose scope is to be determined from the literal and equivalent scope of the claims below: 

We claim:
 1. An apparatus for applying force to a borehole tool from a moving source, comprising: a mandrel having a passage therethrough and an upper and lower ends; an outer housing slidably mounted to said mandrel for predetermined relative movement in opposed directions, said outer housing comprising an outer housing passage which continues said mandrel passage; said mandrel and outer housing defining a first variable volume chamber which communicates with said passage such the pressure in said first variable volume chamber results in a force applied to the borehole tool that is insensitive to said predetermined relative movement.
 2. The apparatus of claim 1, wherein: pressure in said chamber arises from flow resistance in the borehole tool.
 3. The apparatus of claim 1, further comprising: a second variable volume chamber communicating to outside said outer housing; said variable volume chambers comprise opposed piston faces to create a net force on the borehole tool.
 4. The apparatus of claim 1, wherein: said mandrel and said outer housing are rotationally locked.
 5. The apparatus of claim 4, wherein: said rotational locking comprises a keyway on one of said mandrel and said outer housing engaged to a tab on the other of said mandrel and said housing.
 6. The apparatus of claim 3, wherein: said first variable volume chamber is closer to said uphole end of said mandrel than said second variable volume chamber.
 7. The apparatus of claim 3, wherein: said first variable volume chamber is further from said uphole end of said mandrel than said second variable volume chamber.
 8. The apparatus of claim 6, wherein: pressure in said first variable volume chamber creates a tensile force on the borehole tool.
 9. The apparatus of claim 7, wherein: pressure in said first variable volume chamber creates a compressive force on the borehole tool.
 10. The apparatus of claim 6, wherein: one of said mandrel and said outer housing comprising opposed surfaces that define said predetermined relative movement.
 11. The apparatus of claim 7, wherein: one of said mandrel and said outer housing comprising opposed surfaces that define said predetermined relative movement.
 12. The apparatus of claim 3, wherein: said first and second variable volume chambers defined by an upper seal, a middle seal and a lower seal.
 13. The apparatus of claim 12, wherein: said first variable volume chamber communicating with said passage between said upper and middle seals and said second variable volume chamber communicating with outside of said outer housing between said middle and lower seals.
 14. The apparatus of claim 12, wherein: said first variable volume chamber communicating with said passage between said middle and lower seals and said second variable volume chamber communicating with outside of said outer housing between said upper and said middle seals.
 15. The apparatus of claim 10, wherein: said mandrel and said outer housing move in tandem after one of said opposed surfaces are engaged.
 16. The apparatus of claim 11, wherein: said mandrel and said outer housing move in tandem after one of said opposed surfaces are engaged.
 17. The apparatus of claim 10, wherein: said opposed surfaces are located in said first variable volume chamber.
 18. The apparatus of claim 11, wherein: said opposed surfaces are located in said first variable volume chamber.
 19. The apparatus of claim 1, wherein: said mandrel is connected to the borehole tool and said outer housing is connected to the moving source.
 20. The apparatus of claim 1, wherein: said first variable volume chamber is located between said outer housing passage and said mandrel passage.
 21. The apparatus of claim 20, wherein: said mandrel comprising a seal to said outer housing to allow said mandrel to act as a piston exerting a force on the borehole tool.
 22. The apparatus of claim 21, wherein: said outer housing comprising opposed surfaces that act as travel stops in opposed directions for said mandrel.
 23. The apparatus of claim 1, wherein: pressure in said passages is created by flow restriction through the borehole tool which communicates with said first variable volume chamber to put a force on said mandrel in the direction of the borehole tool. 